Tyrosinemia type 1 (HT 1) is an autosomal recessive metabolic disease caused by deficiency of fumarylacetoacetate hydrolase (FAH). Its main clinical features include progressive liver failure, renal tubular damage neurological crisis and liver cancer. The PI and his colleagues have created a murine model of FAH deficiency by gene knockout in embryonic stem cells. Affected animals display a complex phenotype of hepatic dysfunction and neonatal death. They have shown that the drug NTBC, an inhibitor of p-hydroxyphenylpyruvate dioxygenase, corrects the liver disease and neonatal lethality of mutant mice. Withdrawal of this medication at a later age gives rise to a phenotype similar to human HT 1 and these older animals therefore represent a model in which dietary, pharmacological, transplantation and gene transfer therapies can be tested. Because NTBC treated animals still develop tumors, the investigators will test whether the combination of NTBC with a low tyrosine diet and/or antioxidant treatment can improve outcome. They have recently shown that metabolically corrected hepatocytes have a selective growth advantage over deficient cells in FAH mutant liver. Therefore, replacement of even a small portion of mutant hepatocytes with FAH expressing cells leads to a normalization of the majority of liver tissue over time. The group will determine whether therapy by a) transplantation of wild type hepatocytes or b) virally mediated gene transfer into FAH deficient animals can cure HT1, especially in terms of cancer development and renal disease. Viral gene transfer strategies will include in vivo and ex vivo use of adenoviral vectors. Adenoviral vectors will be used to test the concept of in vivo homologous recombination for the correction of a genetic defect (gene replacement therapy). The investigators will test whether FAH can be used as a selectable marker in non FAH deficient mice, a strategy potentially useful in all liver gene therapy. Accumulation of the hepatotoxic substrates of FAH will be induced by administration of substrate precursor or specific FAH inhibitors and in vivo selection will be monitored.